He needs rest. He has been injured. He gets frustrated when he plays poorly and excited when he makes a big play. He even has a bad game occasionally.

Still, doubts remain. Duncan has been so steady, so straight-faced, so clinical in his execution over his 17-year career, he has half-jokingly been called a basketball cyborg. If he one day malfunctioned on the court, revealing a network of interior chips and wiring, most people would be surprised not because he was an android, but because he malfunctioned.

At 37 years old, he is still capable of being a force. He showed that Monday against the Boston Celtics, when he scored 23 of his 25 points in the second half as his San Antonio Spurs ran away with a 104-92 win. Against a stream of younger defenders, Duncan demonstrated his long-held array of offensive moves. He unleashed bank shots, hook shots, step-back jump shots and good old-fashioned dunks to make Jared Sullinger, Brandon Bass, Kris Humphries, Kelly Olynyk and Joel Anthony look like scenery.

“He wasn’t going to be denied,” Celtics coach Brad Stevens said. “We don’t have great matchups for him. There’s not many great matchups for him when he’s going like that in the NBA or the world. We tried just about everybody that we could try, and he still scored at will.”

The easy story on Duncan is that he never got frustrated, despite a two-point first half in which teammate Boris Diaw more than sextupled Duncan’s scoring output. Cyborgs don’t feel frustration, after all. But nobody wins four NBA championships without a raging competitive spirit that makes their blood boil when missed shots pile up like they were for Duncan.